Plant Pigments are molecules that react differentially to white (full spectrum) light. There are three categories
of pigments found in plants:
Porphyrins
chlorophylls are the primary photosynthetic pigments imbedded in the inner
(thylakoid) membranes of chloroplasts … they are slightly different shades of green
Chlorophyll a
Chlorophyll b
Chlorophyll c
Carotenoids
chloroplasts
Carotene
Lycopene
Xanthophyll
accessory pigments found alongside chlorophyll in the thylakoid membrane of
- this one is orange, like a carrot
- this is red, lots of it in ripe tomatoes
- this one is yellow
Flavanoids
accessory pigments found in plant cell vacuoles, their color is dependent on the
specific and amount of carbohydrates (mostly sugars), and on pH. Colors range from blue to purple to red to
pink
Flavonol
Anthocyanin
ALL photosynthetic organisms contain one or more chlorophylls. ALL land plants as well as the "green algae"
contain chlorophylls a and b as their primary photosynthetic pigments.
Accessory pigments perform a variety of functions for the plant. They can assist in the photosynthesis process
(carotene, xanthophylls) or they can attract pollinators in flowers or seed dispersing animals in ripe fruits. Birds
see red, so any flower or fruit that is attractive to birds is red. To say it a different way, if a flower or fruit is not
red, it is unlikely to be noticed by birds. Go figure.
Some leaves that contain chlorophyll appear different in color because the green color of chlorophyll is masked
by accessory pigments such as anthocyanins. The red leaves of some ornamental maple trees appear red for this
reason. Many plants have leaves that appear to be a color other than green. But the green is hiding.
In the fall in temperate regions (4 seasons), pigments are broken down as plants sense the onset of winter.
Chlorophyll breaks down faster than other pigments, and whereas it masks the yellow, orange, and red pigments
during the growing season, those other pigments become increasingly visible in the fall. So the leaves don't
really change color (though they certainly appear to do so), rather, they simply subtract lots of green and the
"hidden" colors are allowed to show themselves. This can be beautiful and inspiring.
Role in photosynthesis: Chlorophylls accept light (photons) at specific wavelengths and this causes electrons
to get all excited and jump off the molecule and start moving. A steady stream of electrons moving along from
one molecule to another generates energy to drive photosynthesis. As electrons move along, they lose energy,
and sometimes accessory pigments can boost the energy level of the electrons to keep them moving.
Factoids: Pigments can be good for you. Carotene is just a few tweaks away from vitamin A, and we can
make vitamin A from carotenes. Other pigments appear to have properties that are really good for you for
reasons that I can't explain. The tomato plant Solanum lycopersicum produces fruits high in lycopenes (thus the
name). Since scientists discovered this, ketchup makers began to tout the health benefits. If you eat lots of
foods high in carotene, your skin will appear more yellow. Carotene is important for making the pigments in
the eyes, and that's why your mother always tells you to eat your carrots so you can see better. That's actually
true. In poor countries where diets are low in carotene-rich vegetables, blindness is a significant problem.